KR20180112021A - Vector Self-ECG Inspection Method and Vector Self-ECG Inspection System - Google Patents

Abstract

The present invention relates to a vector self-electrocardiographic examination method and a vector self-electrocardiographic examination system for performing the method. It is an object of the present invention to provide an improved electrocardiographic method, particularly considering the diagnosis of ischemic heart disease. The method of the present invention involves calculating the orientation of an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) in relation to a reference direction independent of the patient or heart position to calculate the vector magnetic cardiogram.

Description

Vector Self-ECG Inspection Method and Vector Self-ECG Inspection System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vector self-electrocardiography (ECG) examination system for performing a vector magnetic resonance imaging (ECG) examination method and method.

(MCG) is a non-invasive method for recording the magnetic field generated by the electrical activity of the heart, for example, heart disease such as ischemic heart disease (IHD; for example, [2], [ 8], [10], [13], [14]).

Although recently used frequently, self-examination of electrocardiogram still has considerable disadvantages considering IHD diagnosis. For example, parameters used for diagnostics, including magnetic field slope [6], magnetic map angle [12], and evaluation of different segments of a butterfly plot [7], typically appeared in the sensor space. One major disadvantage of evaluating all parameters in the sensor space is system dependency, i.e. no direct comparison between different MCG devices is possible. Moreover, whenever the system is modified, diagnostic parameters must be updated by performing additional clinical studies.

Another disadvantage of the known method is statistically significant for the detection of ischemia, but its variance is still too high for clinical applications. A further problem with conventional diagnostic methods is that the magnetic field gradient is not well defined in the presence of a monopole-like magnetic field. These magnetic fields are associated with myocardial ischemia, and thus diagnostic methods aiming at ischemia should be powerful under these circumstances. Attempts have been made to diagnose ischemia in the source space using pseudocurrent mappings [9]. It is possible to calculate the pseudo current map in the source space by the minimum reference estimate [11]. However, the source space map has disadvantages similar to the sensor space map, introducing additional errors from the pseudo inverse method.

A vector electrocardiographic examination (VMCG) is a self-electrocardiogram method in which all three quadrature components of a magnetic cardiac vector are measured at the same location (see, for example, [10]). The VMCG can be used to reconstruct changes in direction and intensity of magnetic cardiac vectors over time, e.g. during cardiac cycles.

It is an object of the present invention to provide an improved electrocardiographic method, particularly considering the diagnosis of ischemic heart disease. In particular, it is an object of the present invention to provide a self-electrocardiographic method with little or no system dependency and rate of change.

In one aspect, the problem is solved by a vector self-electrocardiography method,

a. Measuring the amplitude and direction of the three quadrature components of the magnetic field (s) produced by the subject's heart during the cardiac activity cycle using one or more magnetic field sensors,

b. Positioning a reference source position for cardiac magnetic and / or electrical activity, using data measured in step a, wherein the reference source position is suitable for indicating a source of magnetic and / or electrical activity during the cardiac activity period, A point source that does not need to be inside the heart volume,

c. Evaluating a reference direction from the data measured in step a, wherein the reference direction is a magnetic moment at a myocardial volume during a period of magnetic and / or electrical cardiac activity with a known direction of magnetic moment and / or current with respect to cardiac anatomy and / RTI > and / or < RTI ID = 0.0 >

d. Computing an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) at a reference source location located in step b, from the measured data in step a, said ESCS or ESMS being calculated from said reference Calculating an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) representing an electrical heart vector (EHV) or a magnetic heart vector (MHV)

e. Registering the EHV and / or MHV calculated in step d during at least a portion of cardiac activity in the vector electrocardiogram.

By considering the position of the heart and using a suitable inverse solution, for example, multipole expansion in the source space, the present invention solves the problem of instability of system dependency, rate of parameter change and gradient of magnetic field gradient. The method of the present invention is particularly suitable for providing information for diagnosing cardiac ischemia.

The inventors have found that an attempt is made to solve the inverse problem using the insufficient limitation on the source for the main reason for the failure of the pseudo-current mapping in the source space. The normal pseudo current map is composed of a grid of, for example, a 16 x 16 (or even larger) micro current source. Each current source has two degrees of freedom (amplitude in the x- and y-directions). This means that a solution for a total of more than 512 parameters should be found. For example, for 64 channels of the current MCG system, the maximum number of eigenvalues for the pseudo-inverse of the lead-field matrix is 64 if the channels are completely independent, This is not the case in this case because some eigenvalues must be removed in consideration of noise. However, this number is not enough to fit 512 parameters and find a unique solution to the inverse problem.

Instead of a map, the present invention uses a single point source, e.g. a single magnetic multipole source, preferably a single dipole source, so that the number of degrees of freedom is manageable (in the case of a dipole source, Degrees of freedom of orientation), fewer independent eigenvalues are required to find a unique solution to the inverse problem. For example, while it is desirable to use a single magnetic dipole source, it is also possible to use other single sources, e.g., a single microcurrent source. The inherent problem for this method, that is, the robust dependence of the resulting solution from the location of this single source, is illustrated by the present invention in that it provides a powerful way to identify the optimal location.

In this context, it should be noted that this single point source does not represent any actual physical activity of the heart, but rather an approximation of volumetric electrical activity by an equivalent single magnetic or electrical source (ESMS, ESCS), point magnetic or electrical activity do. The point source is not necessarily located within the heart volume, since it is considered to represent the source for the heart's magnetic and / or electrical activity. It is most likely to be placed inside the heart volume, but it can be placed near the heart, i.e., outside the heart, e.g., below the actual heart (rear, i.e. lower on the z-axis).

The present invention preferably involves taking the measured data during appropriate electrical and / or magnetic cardiac activity and looking for an optimal ESMS or ESCS through an inverse solution of the magnetic field equation. To find the best location for the point source, ESMS or ESCS, for example, a classic pseudo current map in source space may be used. For example, a magnetic field map may also be used. Those skilled in the art are aware of known methods for calculating such pseudo currents or magnetic field maps. In general, any time interval with electrical and / or magnetic cardiac activity may be taken to locate the point source. However, it is desirable to take time intervals with strong electrical and / or magnetic activity. More preferably, the time to exhibit the most potent electrical / magnetic activity during a strong electrical / magnetic activity period in the heart, such as at T _max , during R peak or T peak, The interval is used. For example, the position of the strongest current in this map is taken to determine the optimal location of the point source. It should be noted that since any self-activity reflects the underlying electrical activity, the location of any ESMS corresponds to the location of an equivalent single current source (ESCS). Therefore, in the method of the present invention, ESCS can be used instead of or in addition to ESMS. In addition, although the measured signal derived from the electrical / magnetic activity area of the heart is used to find the optimal location of the point source, the point source itself does not necessarily have to point to a point in this area or even within the heart It should be understood.

When an optimal position is found, the inverse solution can be calculated for each time point during the cardiac activity cycle using ESMS (or ESCS). Since ESMS represents the magnetic heart vector (MHV), registering this change in the vector with respect to intensity (amplitude) and direction over time is a way of representing the MCG measurement, and a vector self-electrocardiogram (vector MCG) or The term VMCG is used in this method.

Thus, the present invention provides a robust and stable method of registering the direction and amplitude of cardiac magnetic activity in the event that the magnetic field gradient method fails.

Since the current MCG system measures the entire heart beat (sinusoidal rhythm), one possible way to represent the VMCG is to track the measurement interval or segment, where each segment of the trace has the next magnetic moment Vector. The amplitude of the vector may be expressed, for example, by the length of the vector. Then, in a single diagram, we can observe the angular and amplitude variations for the whole heartbeat.

The present invention also describes a large rate of change in the current angle even in healthy subjects. The two factors contribute to the large rate of change in angle. First, the position of the patient on the bed under the Dewar changes with each measurement. Second, the location of the heart inside the body varies from person to person. Although strict procedures can account for the first factor and imaging methods such as CT scan or MRI can account for the second factor, this represents a very difficult process and removes one of the advantages of MCG: It is independent of the method. The present invention provides a single solution for solving problems arising from these factors.

The direction may be given by an angle from some reference direction. In the prior art method, the positive x-axis is typically used as a reference, and the angle in the xy plane, the front plane, is 0 [deg.]. However, in accordance with the present invention, the reference direction is determined only for cardiac anatomy, for example, it is determined to always point to the apex of the heart, so it is determined independently of the patient or heart position. As a result, the measured angle is invariant to the patient and the heart position.

In the literature (see, for example, [10]), it is known that the direction of the heart's current during the R peak is toward the apex of the ventricle. In addition, during the R peak, the depolarization current is too strong, so that any ischemic damage current has little effect on the VMCG's main current vector. Therefore, in a preferred embodiment of the method of the present invention, the VMCG direction during the R peak is selected as the reference direction and set to 0 DEG. The VMCG recorded by the method of the present invention is unaffected by the drawbacks of the pseudo-current mapping and is not affected by external factors such as patient and cardiac location for the MCG device.

The term "magnetic field sensor" as used herein refers to a sensor capable of measuring a magnetic field. In accordance with the present invention, one or more magnetic field sensors are used to measure both the direction and magnitude (amplitude) of the magnetic field. This can be done, for example, by a single 3-axis magnetic field sensor, a plurality of (array) 3-axis magnetic field sensors, or a plurality of (array) 1-axis, 2-axis and / or 3-axis magnetic field sensors. A "three-axis magnetic field sensor" is a magnetic field sensor that measures magnetic field components in all three dimensions. The term includes sensors consisting of at least three magnetometers or inclinometers measuring the orthogonal x-, y- and z- components of the magnetic field. The term "1-axis magnetic field sensor" or "2-axis magnetic field sensor" refers to magnetic field sensors that measure only one or two of the three magnetic field components. For example, an array of 1-axis magnetic field sensors oriented in a manner that measures the quadrature components of a magnetic field can also be used to measure both the magnitude and direction of a magnetic field, for example. A SQUID ("superconducting quantum interference device") is preferred as a sensor.

As used herein, a reference to the x-axis associated with a human heart or body corresponds to a reference to the right-left axis and a reference to the y-axis corresponds to a reference to the right- Corresponds to the reference for the head-to-foot axis, and the reference for the z-axis corresponds to the reference for the longitudinal axis.

The term " cardiac activity cycle "relates to any cycle with cardiac activity involving the generation of a magnetic field by current and / or cardiac tissue. In particular, the term relates to the so-called sine wave rhythm, the normal rhythm of the heart, accompanied by atrial and ventricular depolarization and repolarization. In sine wave rhythm, depolarization of the myocardium begins at a cardiogenic node (called a so-called sinusoidal node or SA node) located in the upper right wall of the right atrium, and the atrioventricular nodule between the atria and ventricles of the bundle, AV node). Repolarization of the ventricle terminates the cycle. Atrial and ventricular depolarization and repolarization are reflected by three common wave or wave complexes in normal ECG, P wave, QRS complex and T wave. In ECG, the P wave is generally considered to represent atrial depolarization, and the QRS complex is considered to represent the right ventricle and left ventricular depolarization, and the T wave is considered to represent ventricular repolarization.

The term "appropriate magnetic and / or electrical activity" means that any magnetic and / or electrical activity of the heart can be reliably measured. In particular, the term refers to a sufficiently strong magnetic and / or electrical activity of the heart. In this context, the term "strong" refers to a magnetic and / or electrical signal of the heart that can be reliably measured by an appropriate sensor, i. E. Generating a magnetic and / or electrical signal that can be reliably distinguished from baseline signals and / Or electrical activity. A non-exclusive example of suitable magnetic and / or electrical activity is cardiac activity during the cardiac activity cycle, expressed as the R peak or T peak of the electrocardiogram (ECG).

The term "evaluation of the reference direction" means to determine or identify the direction of magnetic moments and / or currents, using the magnetic or electrical signals measured during the appropriate period of cardiac activity and taking this direction as a reference . The term may indicate, for example, the determination of the average magnetic moment and / or the direction of the current during the R peak of the sinusoidal rhythm of the heart using the sensor data measured during the R peak. This direction may be taken as the " reference direction "and may be set to zero, for example, to act as a reference for calculating the deviation angles of the directions of the magnetic moments and / have.

The term "average direction of magnetic moment and / or current" refers to the average direction of magnetic moment and / or current, taking into account that the heart is a volume conductor.

The term "reference source position" refers to the point taken as the source of all electrical and / or magnetic activity of the heart. Thus, the reference source position is a virtual point electrical and / or magnetic source having parameters such that the magnetic field produced by this reference source is equivalent to the magnetic field measured from the heart volume. It should be noted that the calculated point, the reference source position, may lie within the actual volume source, i.e. within the heart, but also outside the heart volume near the heart.

The term " known direction of magnetic moment and / or current associated with cardiac anatomy "means the direction of the magnetic field and / or current to the physical part of the heart, i.e., the tip of the heart, i.e., the left ventricle apex.

The term " enrollment of EHV and / or MHV during at least a portion of cardiac activity "means that EHV and / or MHV, e. G. EHV and / or MHV, over time during a period of cardiac activity, for example during a sinus rhythm, (Amplitude) and direction of the MHV. The registered data can then be used to construct a magnetron.

The term "inverse solution" means a solution to the inverse problem. Those skilled in the art are familiar with this problem, and with the reverse solution, that is, how to find a solution to reverse problems. In the context of the present invention, the term " inverse solution "refers to the" sensor space ", that is, data measured from outside the heart by each sensor, , And the source is the heart).

The term "subject" as used herein preferably refers to a vertebrate, more preferably a mammal, and most preferably a human.

Steps b through e of the method of the present invention are preferably implemented, for example, by a software algorithm running on a computer.

In a preferred embodiment of the vector magnetic cardiographic examination method of the present invention, in order to locate the reference source position in step b described above, during the strong magnetic and / or electrocardiac activity, preferably the most powerful magnetic And / or data measured during electrical activity is used, for example, to calculate a pseudo current map and / or a magnetic field map. Procedures for computing a pseudo current map or a magnetic field map are known to those skilled in the art. The pseudo current map can be calculated, for example, by using a 16 X 16 grid, as is known in the art. It is particularly preferred to use a time interval with the strongest magnetic and / or electrical activity during the R peak or T peak (e.g. at T _max ), preferably during the R peak, to find the reference source position. The term "during R peak or T peak" refers to the period of cardiac activity that is typically expressed as the R peak or T peak on the ECG.

More preferably, in step c, the reference direction of the magnetic field and / or current in the heart is evaluated during the R peak. Since it is known that the direction of the heart's current during the R peak is pointing towards the apex of the ventricle and the R peak is a period of intense cardiac activity that produces a strong measurable signal, it is desirable to use the R peak to determine the reference direction. However, any other period of magnetic and / or electrical cardiac activity in which the direction of the magnetic field and / or current is known or can be determined in relation to cardiac anatomy is also suitable for establishing a reference direction.

In the vector magnetocardiographic method of the present invention, it is particularly preferred that for both the determination of the reference source position and the evaluation of the reference direction, a period of cardiac activity corresponding to the R peak is used. However, the present invention is not limited to using R peaks for both purposes.

In a further preferred embodiment of the vector magnetocardiographic method of the present invention, the difference in direction and / or magnitude between EHV and / or MHV at different points of the vector ECG is calculated and different points are calculated at different points in time during cardiac sinus rhythm . This is particularly useful for diagnostic purposes. For example, differences in orientation and / or size between EHV and / or MHV at T _max and T _end have been found to indicate cardiac ischemia.

In a further aspect, the invention is directed to a vector self-electrocardiographic system (VMCG system) adapted to perform the method according to the first aspect of the present invention. The vector self-electrocardiographic system of the present invention

a. One or more magnetic field sensors for measuring the direction and magnitude of the three orthogonal components of the magnetic field (s) produced by the subject's heart during the period of cardiac activity,

b. Means for (automatically) locating a reference source position for cardiac magnetic and / or electrical activity, using data measured by the one or more magnetic field sensors, wherein the reference source position is preferably a strong magnetic and / (Or automatically) a reference source position, which is a point source suitable for indicating the source of magnetic and / or electrical activity during the magnetic and / or electrical cardiac activity, using data during the most powerful magnetic and / Means for positioning,

c. Means for (automatically) evaluating a reference orientation (automatically) from data measured by one or more magnetic field sensors, the reference orientation being indicative of a magnetic field and / or an electrical cardiac activity with a known direction of magnetic moment and / Means for (automatically) evaluating a reference direction, which is the average direction of magnetic moments and / or currents in the myocardial volume during a period,

d. As means for (automatically) calculating (automatically) an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) at a reference source location from data measured by one or more magnetic field sensors, ESCS or ESMS Means for (automatically) calculating an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS), which represents an electrical heart vector (EHV) or a magnetic heart vector (MHV)

e. And means for registering EHV and / or MHV during at least a portion of cardiac activity in the vector ECG.

The VMCG system performs the method of the first aspect of the present invention, for example by hard-wiring the algorithm that performs steps (b-e) of the method of the present invention Lt; RTI ID = 0.0 > VMCG < / RTI > However, the VMCG system may also be a standard VMCG system including a computer, e.g., a personal computer, running a computer program that implements an algorithm to perform steps b through e of the method of the present invention.

In the following, the present invention is described more specifically by way of example and with reference to the accompanying drawings for purposes of illustration only.

1 is a schematic diagram for locating a reference source position using a pseudo-current map;
Figure 2 illustrates an exemplary VMCG of a healthy subject constructed using the method of the present invention.
FIG. 3 is a 2-D diagram of the VMCG of FIG. 2 corresponding to an equivalent single current source (ESCS), wherein the given current unit is [A] 4πμ ₀ 10 ^-6 , where μ ₀ is the vacuum permeability.
4 is a 2-D diagram of a VMCG in a patient with single vessel disease in LAD, the current unit of the shaft being the same as in Fig. 3; Fig.

Figure 1 shows a standard pseudo-current map for a 20 x 20 source grid, using 13 eigenvalues to find the optimal location of the ESMS. The pseudo current map was established from the data measured during the R peak of the sinusoidal rhythm. The circled area represents the strongest electric activity area during the R peak.

The VMCG of healthy subjects is shown in FIG. The large loop denoted by reference numeral 1 represents the QRS complex, and includes the R peak 2 and the smaller loop 3 represents the T peak.

Figure 3 shows a 2-D view of the VMCG of Figure 2 corresponding to an equivalent single current source (ESCS). This view is particularly useful for facilitating angle measurements, i.e., changes in the direction of the MHV / EHV. Q, R, S, T and even P waves. The P wave at 125 ms is represented by the number 5, the R peak at 200 ms is represented by the number 2, and the T _max at 339 ms is represented by the number 6. The current direction during full sine wave rhythm is consistent with the literature. Each segment (4) of the VMCG corresponds to the MHV for the same time interval during the sinusoidal rhythm, the length of each segment representing the amplitude of the magnetic field, and the orientation in the direction to the reference direction.

Figure 4 is a 2-D view of the VMCG of a subject with single vessel disease in the left anterior descending artery (LAD) identified by angiography. The current direction during T wave {381 ms to T _max (6)} is off about 180 ° compared to the R peak (at 200 ms).

Quotation

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[8] Helena Hanninen, Panu Takala, Markku Makijarvi, Juha Montonen, Petri Korhonen, Lasse Oikarinen, Jukka Nenonen, Toivo Katila, and Lauri Toivonen. Detection of exercise-induced myocardial ischemia by multichannel magnetocardiography in single vessel coronary artery disease. Annals of noninvasive electrocardiology, 5 (2): 147-157,2000.

[9] Hyun Kyoon Lim, Namsik Chung, Kiwoong Kim, Young-Guk Ko, Hyukchan Kwon, Yong-Ho Lee, Jin-Bae Kim, Jung Rae Cho, Jin-Mok Kim, In-Seon Kim, et al. Reproducibility of quantitative estimation of magnetocardiographic ventricular depolarization and repolarization parameters in patients with coronary artery disease. Annals of biomedical engineering, 35 (1): 59-68, 2007.

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Claims (7)

As a vector self-electrocardiogram method,
a. Measuring the amplitude and direction of three quadrature components of the magnetic field (s) produced by the subject's heart during a cardiac activity cycle using one or more magnetic field sensors,
b. Using a data measured in step (a), to locate a reference source position for cardiac magnetic and / or electrical activity, wherein the reference source position is determined by the source of the magnetic and / or electrical activity during the cardiac activity period Which is a point source suitable for representing a point,
c. Evaluating a reference direction from the data measured in step (a), wherein the reference direction has a known direction of magnetic moment and / or current with respect to cardiac anatomy, Which is an average direction of the magnetic moments and /
d. Calculating an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) at the reference source location located in step (b) from the measured data in step (a) computing an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) representing an electrical heart vector (EHV) or a magnetic heart vector (MHV) with respect to said reference direction evaluated in step c); and
e. Registering the EHV and / or MHV calculated in step (d) during at least a portion of the cardiac activity in the vector self-monitored electrocardiogram
Includes a vector self-electrocardiogram method. The method according to claim 1,
a. During step (b), during the strongest magnetic and / or electrical activity, preferably during the strongest magnetic and / or electrical activity of a strong magnetic and / or electrical cardiac cycle, preferably during the R or T peak, The data being used to locate the reference source location, and / or
b. In step (c), the reference direction of the magnetic field and / or current in the heart is evaluated during the R peak. The method according to claim 1 or 2,
In step (b), the reference source position is located by calculating a pseudo current map and / or a magnetic field map using the data measured in step (a). 4. The method according to any one of claims 1 to 3,
Wherein differences in direction and / or magnitude between the EHV and / or MHV at different points of the vector magnetic cardiogram are calculated, and wherein the different points represent different time points during the cardiac sinus rhythm. The method of claim 4,
Wherein the difference in direction and / or size between said EHV and / or MHV at T _max and T _end is calculated. A vector self-electrocardiograph system for performing the method according to any one of claims 1 to 5. The method of claim 6,
a. One or more magnetic field sensors for measuring the direction and magnitude of the three quadrature components of the magnetic field (s) produced by the subject's heart during a period of cardiac activity,
b. Means for locating a reference source position for cardiac magnetic and / or electrical activity, using data measured by the one or more magnetic field sensors, And / or means for locating a reference source location, which is a point source suitable for indicating said source of electrical activity,
c. Means for evaluating a reference direction from data measured by the one or more magnetic field sensors, the reference direction having a known direction of magnetic moment and / or current in relation to cardiac anatomy, during a period of magnetic and / Means for evaluating a reference direction, which is an average direction of magnetic moments and / or currents in the myocardial volume,
d. Means for calculating an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS) at said reference source location from data measured by one or more magnetic field sensors, said ESCS or ESMS being associated with an electrical Means for calculating an equivalent single current source (ESCS) or an equivalent single magnetic source (ESMS), which represents a heart vector (EHV) or a magnetic heart vector (MHV)
e. Means for registering said EHV and / or MHV during at least a portion of said heart activity in a vector electrocardiogram
Vector electrocardiogram system, containing.

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